Nanotechnology is science and engineering at the scale of atoms and molecules. It is the manipulation and use of materials and devices so tiny that nothing can be built any smaller. Materials at the nanoscale are typically between 0.1 and 100 nanometres (nm) in size - 1 nm is one billionth of a metre (10-9 m).

Most atoms are 0.1 to 0.2 nm wide, strands of DNA are around 2 nm wide, red blood cells are around 7000 nm in diameter, while human hairs are typically 80,000 nm across.

A nanometre is to a centimetre what the length of a human footprint is to the width of the Atlantic Ocean. A nanometre is also about the length human fingernails grow by each second.

2. Why are small things different and what gives them their special properties at the nanoscale?

This is the scale at which the basic functions of the biological world operate - and materials of this size can display strikingly different physical and chemical properties, compared with larger particles of the same material. Scientists are using these unusual properties to create novel materials and technologies.

For example, tiny clusters of atoms of gold and silver show unique catalytic properties, while larger pieces of the same material are relatively inert. Silver is popular in jewellery because it is unreactive and tarnishes slowly, yet at the nanoscale it shows strong antibacterial properties. Nanoparticles of silver are currently being used in new types of wound dressing.

Nanocrystalised metals, such as iron, are much stronger and more flexible than conventional varieties.

These properties are largely due to two factors. Smaller particles have a relatively larger surface area, compared with their volume, making them much more chemically reactive. In addition - at scales below 100 nm - the weird quantum effects of the atomic world start to take hold. Quantum effects can change the optical, electronic or magnetic qualities of materials in unpredictable ways.

"It's not that new laws of nature are being discovered," says nanotechnologist Uzi Landman of the Georgia Institute of Technology in Atlanta, US, "but a reduction in size brings about differences in how familiar laws of physics play out at a small scale".

Trying to squeeze an electron along a 1 nm nanowire, for example, restricts its movement and activity since you are approaching the size of the wavelength of the electron, says Landman. This manifests itself in a strange relationship between voltage and conductance at small scales.

Small crystals of some materials become stronger because they simply reach the point where they can not translocate or fracture in the same way as larger crystals when pressure is applied to them. Metals become more like plastics in some ways, Landman adds.

In addition, small clusters of material are able to undergo unusual structural changes that enable chemical reactions, and therefore account for some of the novel catalytic properties they develop.

A small cluster of gold can "move like an amoeba," says Landman. His research has shown that the catalytic property of gold clusters can even change along with the configuration of atoms in those clusters. For example, eight- or 22-atom gold particles are catalytic, while those made up of seven or 20 atoms are inert.

3. What are some potential applications for nanotechnology?

If you can name it, nanotech might be able to do it.

Back in 1986, futurist K Eric Drexler (now of the Foresight Institute - a US nanotech think tank) imagined a utopian future where self-replicating nanoscale robots, or nanobots, carry out most of the work in society. Furthermore these tiny machines would repair and maintain the human body from the inside out, making humans virtually immortal. They would also float and swim free in the environment, mopping up pollution and generally sprucing things up as they go.

More realistically in the short term, nanotechnology will lead to important advances in computing, medicine and technologies to benefit the environment and military science.

One group at Rice University in Houston, US, has successfully used tiny gold-plated "nanobullets" to seek out and destroy inoperable cancers. The scientists attach the particles to antibodies which only bind to tumour cells. The "nanobullets" later heat up when near-infrared light is fired at them, through the body, killing the cancerous tissue in the process.

Other researchers with the US-army-funded Institute for Soldier Nanotechnologies at MIT in Cambridge, US, are in the process of developing nanoscience-enhanced battle-suits. Their remit is to develop fabrics that can morph to improve camouflage, stiffen to splint broken bones and even deflect bullets and the energy from explosions.

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